It has long been known that the capacity of dynamoelectric machines, whether utilized as generators or as motors, can be considerably increased if the components thereof are cooled. Of various cooling schemes available, liquid cooling is preferred over gas cooling because of the typically greater heat capacity of a given volume of liquid coolant over a gaseous coolant.
Liquid cooling of the machine stator does not provide a particular difficulty since stator components are stationary and it is a relatively simple matter to establish the requisite connections for a liquid flow path throughout the stator sufficient to provide the desired degree of cooling. Conversely, cooling rotor component presents more of a problem in that means for conducting the coolant from a stationary part of the machine to the rotor are required; and this typically requires couplings, unions or any of a variety of other known means.
Such structure increases the complexity of the apparatus and can result in a loss of machine efficiency. In particular, if the liquid coolant is permitted to leak at the transfer point from stationary machine components to rotating machine components, there is a strong possibility, and even a probability that the liquid will be driven to the air gap between the rotor and the stator armature which will result in so-called "windage losses".
Another difficulty that may be encountered in liquid cooled rotors occurs when, for some reason, the coolant supply is temporarily interrupted. Notwithstanding such interruption, heat will continue to be generated within the rotor. Should the build-up become too great over the period of interruption of coolant flow to the rotor, severe damage to the machine will result.
The present invention is directed to overcoming one or more of the above problems.